The long-term goal of the ongoing research in this laboratory is to understanding the involvement of the cell surface in early mammalian developmet. The objective of the proposed research is to characterize the synthesis, cell surface expression and function of the BL glycoprotein antigen during mouse preimplantation development. BL is an embryo-specific, stage-specific glycoprotine antigen which is synthesized by the early mouse embryo, appears on the cell surface during the preimplantation period, and appears to be functionally involved in development. Early mouse embryos possess little rough endoplasmic reticulum or Golgi material and are, therefore, deficient in the organelles normally involved in the synthesis of such a surface glycoprotein. Recent EM cytochemical evidence that these BL antigens are localized exclusively in the cortex of early mouse embryos, a region containing many free polysomes and some small vesicles; ER and Golgi when observed are always negative for BL. The following specific aims are proposed: (1) To study the synthesis glycosylation and translocation to the surface of the BL glycoprotein antigen and other selected antigens by ultrastructural immunochemistry, gel analysis and immunofluorescence. This will provide insight on a possibly unique cortical pathway for a surface glycoprotein. (2) To investigate the mechanism(s) for the maintenance of the cortical localization of BL. This will lead to a better understanding of cell polarization and the maintenance of membrane domains. (3) To determine whether a specific morphogenetic or biochemical defect results when BL surface expression is blocked by the microinjection of antibody to BL. (4) To determine when in oogenesis, translation of BL maternal mRNA first occurs and whether this message remains the only source of BL mRNA used by the embryo after fertilization. This will provide information on the transcriptional control of an embryo-specific cell surface glycoprotein. (5) To ascertain whether the disappearance of BL antigens at the blastocyst stage is due to release of the antigen from the surface, internalization, or antigenic alteration, and whether this loss is tied to the morphogenetic event of blastocoel formation. This will give insight into the mechanisms used for modulation of surface antigen expression in preimplantation embryos. The results from all the proposed experiments will give us insight into normal and abnormal development and may be relevant to potential contraceptive mechanisms.